In the modern society to today, main sources of energy have been fossil fuel, nuclear energy and waterpower. However, as these energy sources are being exhausted and may cause environmental problems, many countries have attempted develop an alternative energy.
Recently, as the role of an alternative energy increases due to the drastic rise in oil price and more strict environmental regulations by UNFCC (the United Nations Framework Convention on Climate Change), a fuel cell has been spotlighted as the next-generation energy source.
The fuel cell is a device that can convert chemical energy of a fuel to electric energy. Unlike others, the fuel cell is not restricted by Carnot cycle, thus showing a remarkably high efficiency and generates relatively less noise, vibration and waste gas. The fuel cell may also generate electric energy continuously as long as fuel and oxidant are supplied. Depending on the kind of electrolyte and the operation temperature, it may be divided into alkali fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), polymer electrolyte membrane fuel cell (PEMFC), solid oxide fuel cell (SOFC), direct methanol fuel cell (DMFC), etc.
In particular, polymer electrolyte membrane fuel cell (PEMFC) shows a rapid start-up due to a low operation temperature and is easy to manufacture using a solid electrolyte. In addition, it has superior output density and energy conversion efficiency. For these reasons, it has been intensively studied for portable, home and military uses or as an electric source of a car or an energy source for distributed generation.
FIG. 1 shows the principle of a polymer electrolyte membrane fuel cell (PEMFC). Protons produced when hydrogen is oxidized in an anode react with oxygen in a cathode, thus generating water and electricity.
Currently most popular fuel cell polymer electrolyte membrane is Nafion, which is a perfluorosulfonic acid based polymer. Nafion, however, has serious drawbacks of high price and deterioration of cell performance at a temperature of higher than 80° C. due to the decrease in proton conductivity caused by dehydration of membrane. Therefore, PEMFC, which includes an aqueous system, shows a serious deterioration of electrode deactivation due to a low operation temperature and the poisoning caused by carbon monoxide (CO). Further, this requires an additional water management for humidifying the membrane, thus decreasing the productivity of the fuel cell and preventing the commercialization of the fuel cell.
To overcome the aforementioned problems, there have been attempts made to use materials that are superior in proton conductivity, electrochemical stability and thermal stability even under a high temperature non-aqueous condition as a polymer electrolyte of a fuel cell. Among these attempts, Japanese patent application publication No. 2000-195528 discloses a method of doping phosphoric acid in polybenzimidazole-based polymer electrolyte. However, this method has a problem that water produced on a cathode causes the elution of phosphoric acid, resulting in decrease in the proton conductivity of electrolyte membrane.
Therefore, there is a need for a new non-aqueous polymer electrolyte that has a decreased price and improved high-temperature stability, salvation stability and/or electrochemical stability.
The above information disclosed in this Background Art section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.